🎰 Slotscheck

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Adding __slots__ to a class in Python is a great way to improve performance.
But to work properly, all base classes need to implement it — without overlap!
It's easy to get wrong, and what's worse: there is nothing warning you that you messed up.

✨ Until now! ✨

slotscheck helps you validate your slots are working properly.
You can even use it to enforce the use of slots across (parts of) your codebase.

See my blog post <https://dev.arie.bovenberg.net/blog/finding-broken-slots-in-popular-python-libraries/>_
for the origin story behind slotscheck.

Quickstart

Usage is quick from the command line:

.. code-block:: bash

python -m slotscheck [FILES]...

or

slotscheck -m [MODULES]...

For example:

.. code-block:: bash

$ slotscheck -m sanic
ERROR: 'sanic.app:Sanic' defines overlapping slots.
ERROR: 'sanic.response:HTTPResponse' has slots but superclass does not.
Oh no, found some problems!
Scanned 72 module(s), 111 class(es).

Now get to fixing —
and add slotscheck to your CI pipeline or
pre-commit <https://slotscheck.rtfd.io/en/latest/advanced.html#pre-commit-hook>_
to prevent mistakes from creeping in again!
See here <https://github.com/Instagram/LibCST/pull/615>__ and
here <https://github.com/dry-python/returns/pull/1233>__ for examples.

Features

Detect broken slots inheritance
Detect overlapping slots
Detect duplicate slots
Pre-commit <https://slotscheck.rtfd.io/en/latest/advanced.html#pre-commit-hook>_ hook
(Optionally) enforce the use of slots

See the documentation <https://slotscheck.rtfd.io>_ for more details
and configuration options.

Why not a flake8 plugin?

Flake8 plugins need to work without running the code.
Many libraries use conditional imports, star imports, re-exports,
and define slots with decorators or metaclasses.
This all but requires running the code to determine the slots and class tree.

There's an issue <https://github.com/ariebovenberg/slotscheck/issues/6>_
to discuss the matter.

Notes

slotscheck will try to import all submodules of the given package.
If there are scripts without if __name__ == "__main__": blocks,
they may be executed.
Even in the case that slots are not inherited properly,
there may still be an advantage to using them
(i.e. attribute access speed and some memory savings).
However, in most cases this is unintentional.
slotscheck allows you to ignore specific cases.
Because slotscheck imports your code in arbitrary order,
it can—in rare cases—result in confusing and randomly-occurring import errors
in third-party libraries.
In such a case, it is recommended to omit modules such as your tests
and mypy plugins from the slotscheck run.
See here <https://github.com/ariebovenberg/slotscheck/issues/178>.
Alternatively, you can use PYTHONHASHSEED=<any value> to make the import order deterministic.
A solution to this problem is being worked on in this issue <https://github.com/ariebovenberg/slotscheck/issues/270>.

Installation

It's available on PyPI.

.. code-block:: bash

pip install slotscheck

Dependencies of slotscheck (2).
Dependency	Optional
click	false
tomli	false

Package profile

slotscheck

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